This invention generally relates to methods of treating hematopoietic stem cells (HSCs) for improving their therapeutic usefulness and more particularly, but not limited to, treating hematopoietic stem cells derived from cord blood, and hematopoietic stem cells thus treated.
During inflammation, P-selectin and E-selectin cooperatively mediate leukocyte rolling and adhesion on vascular surfaces (McEver, R. P. Selectins: lectins that initiate cell adhesion under flow. Curr Opin Cell Biol. 2002 October; 14:581-856). In the process of bone marrow transplantation, P-selectin and E-selectin also mediate the homing of intravenously injected HSCs to bone marrow. (Frenette, P. S., Subbarao, S., Mazo, I. B., Von Andrian, U. H., Wagner, D. D. Endothelial selectins and vascular cell adhesion molecule-1 promote hematopoietic progenitor homing to bone marrow. Proc. Natl. Acad. Sci. USA. 1998; 95:14423-14428). In most tissues, P-selectin and E-selectin are expressed on endothelial cells after stimulation of agonists, but they are expressed constitutively on bone marrow endothelial cells. Selectins use α2,3-sialylated and α1,3-fucosylated glycans such as sialyl Lewisx (sLex) on glycoproteins or glycolipids as ligands. P-selectin binds to the N-terminal region of P-selectin glycoprotein ligand-1 (PSGL-1), which contains tyrosine sulfates and an O-glycan capped with sLex. E-selectin binds to one or more different sites on PSGL-1. To interact with E-selectin, PSGL-1 does not require tyrosine sulfation, but expression of sLex on O-glycans enhances binding. E-selectin also interacts with other ligands on HSCs. An isoform of CD44 on HSCs has been shown to bind to E-selectin in vitro (Dimitroff, C. J., Lee, J. Y., Rafii, S., Fuhlbrigge, R. C., Sackstein, R. CD44 is a major E-selectin ligand on human hematopoietic progenitor cells. J. Cell Biol. Jun. 11, 2001; 153:1277-1286). Another potential ligand for E-selectin on HSCs is E-selectin ligand-1 (ESL-1) (Wild, M. K., Huang, M. C., Schulze-Horsel, U., van Der Merwe, P. A., Vestweber, D. Affinity, kinetics, and thermodynamics of E-selectin binding to E-selectin ligand-1. J Biol. Chem. 2001 Aug. 24; 276:31602-31612). Each of these glycoprotein ligands is thought to carry sLex structures.
Hematopoietic stem cells harvested from one individual can be transplanted to the bone marrow of another individual following an intravenous infusion. The approach has been widely used in treatment of various hematological disorders such as leukemia (Thomas, E. D. History, current results, and research in marrow transplantation. Perspectives Biol. Med. 38:230-237.1995). Clinically, human HSCs are obtained from three different sources: bone marrow, adult peripheral blood after mobilization, and cord blood obtained from umbilical cords after delivery. Although there are more than 5 million unrelated bone marrow volunteer donors registered worldwide, finding a fully human leukocyte antigen (HLA)-matched unrelated donor remains a problem for many patients because of HLA polymorphism. Compared with bone marrow and adult peripheral blood, cord blood has several potential advantages, in particular the wide and rapid availability of cells and less stringent requirements for HLA identity between donor and recipient because of the lower risk of acute and chronic graft-versus-host disease (GVHD) (Rocha, V., et. al., Comparison of outcomes of unrelated bone marrow and umbilical cord blood transplants in children with acute leukemia. Blood. 97:2962-71.2001). Potential advantages of transplantation using cord blood HSCs rather than HSCs from bone marrow or adult peripheral blood include: (1) a large potential donor pool; (2) rapid availability, since the cord blood has been prescreened and tested; (3) greater racial diversity can be attained in the banks by focusing collection efforts on hospitals where children of under represented ethnic backgrounds are born; (4) reduced risk or discomfort for the donor; (5) rare contamination by viruses; and (6) lower risk of graft-versus-host disease (wherein the donor's cells attack the patient's organs and tissues), even for recipients with a less-than-perfect tissue match. Thus, cord blood-derived HSCs have been increasingly used for bone marrow transplantation in recent years.
In the transplantation setting, the intravenously infused HSCs specifically extravasate in the bone marrow to engraft and proliferate, a process that is defined as HSC homing. Homing has been studied extensively both in vivo and in vitro and is believed to rely on adhesion molecule interactions between HSCs and endothelium of bone marrow. Selectins are a group of adhesion molecules containing a N-terminal carbohydrate-recognition domain related to those in Ca++-dependent (C-type) animal lectins. P-selectin, expressed on activated platelets and endothelial cells, and E-selectin, expressed on activated endothelial cells, bind to glycoconjugate ligands on leukocytes and HSCS. The best-characterized glycoprotein ligand is PSGL-1, a mucin with many sialylated and fucosylated O-linked oligosaccharides. PSGL-1 is expressed on leukocytes and HSCs. Studies with PSGL-1-deficient mice have shown that PSGL-1 mediates leukocyte tethering to and rolling on P-selectin and supports tethering to E-selectin in flow. PSGL-1 also binds to L-selectin, which initiates leukocyte-leukocyte interactions that amplify leukocyte rolling on inflamed endothelial cell surfaces. In human PSGL-1, the P-selectin and L-selectin binding site comprises a peptide sequence containing three tyrosine sulfate residues near a threonine to which is attached a specific branched, fucosylated core-2 O-glycan (McEver, R. P., Cummings, R. D. Role of PSGL-1 binding to selectins in leukocyte recruitment. J Clin Invest. 100:S97-103. 1997; R. P. McEver: Selectins: Ligands that initiate cell adhesion under flow. Curr. Op. in Cell Biol. 14: 581-586, 2002). The fucose moiety is essential for P-selectin binding as measured by in vitro assays using synthetic glycosulfopeptides. The fucosylation is catalyzed by a family of α1,3-fucosyltransferases. Among them, α1,3-fucosyltransferase IV (FT-IV) and α1,3-fucosyltransferase VII (FT-VII) are primarily expressed in human leukocytes. These enzymes catalyze the transfer of a fucose residue from a donor, e.g., GDP-fucose, to an acceptor in α1,3-linkage to GlcNAc in Gal-GlcNAc-sequences. Both FR-IV and FT-VII make the fucose addition which is necessary to form the sLex structure (NeuAcα2,3Galβ1,4[Fucα1,3]GlcNAcβ1-R). The sLex on a core-2 O-glycan attached to a specific threonine in the N-terminal amino acid sequence of human PSGL-1 is critical for binding to P-selectin.
HSCs have the potential to differentiate into different lineages of hematopoietic cells such as red blood cells, myeloid cells, lymphocytes and platelets. Human HSCs express a surface glycoprotein, CD34, which is routinely used for HSC identification and separation. Such human CD34+ cells (cells which express CD34 antigen) represent a heterogeneous population of progenitors with various degrees of hematopoietic maturation. The absence of (“−”) or reduced (“low”) expression of another surface protein, CD38, on human CD34+ cells is considered to be a surrogate marker of a primitive subpopulation of CD34+ cells. Thus, the cells of the CD34+CD38low/− sub-population, which comprise approximately 10-20% of the total CD34+ cells from bone marrow or adult peripheral blood, are highly enriched for multiprogenitor and stem cell activity, including engraftment ability. Notably, approximately 30% of cord blood HSCs are CD34+CD38low/−. However, unlike CD34+CD38low/− adult peripheral blood stem cells, cord blood CD34+CD38low/− HSCs are known to have reduced homing to murine bone marrow, which is primarily dependent on interactions of human HSCs with murine P-selectin on the microvascular endothelium (Hidalgo, A., Weiss, L. A., and Frenette, P. S. Functional selectin ligands mediating human CD34+ cell interaction with bone marrow endothelium are enhanced postnatally. Adhesion pathways mediating hematopoietic progenitor cell homing to bone marrow. J. Clin. Invest. 110:559-569. 2002). Flow cytometry analyses indicate that this homing defect results from non-functional PSGL-1 expressed on these CD34+CD38low/− cord-blood derived HSCs. Thus, the impaired ability of the CD34+CD38low/− HSCs to bind to P-selectin explains in at least in part the delayed platelet and myeloid engraftment associated with cord blood HSC transplantation. The use of cord blood HSCs for transplantation has been primarily restricted to children (which require fewer cells for transplantation) due to the limited quantities and defective homing ability of HSCs isolated from umbilical cords.
An invention which corrects the homing defect of HSCs would significantly increase the potential of umbilical cord blood as a source of hematopoietic stem cells and would thereby lead to lower risks for acute and chronic graft-versus-host disease and improved success of bone marrow reconstitution.